1. Technical Field
The present invention relates to a projector that projects an image to be enlarged, and more particularly, to a technology for cooling down heat emission portions in a projector.
2. Related Art
A projector has been known in which a discharge lamp, such as a high pressure discharge lamp or a metal halide lamp, is used as a light source, light emitted from the light source is modulated by light modulating elements according to an image signal, and the modulation light displaying the modulated image is projected to be enlarged. A plurality of heat emission portions exist in the projector. Specifically, as the plurality of heat emission portions, the projector includes the discharge lamp that functions as the light source, a lamp driving unit that turns on the discharge lamp and maintains a turned-on state of the discharge lamp, light modulating elements, such as transmissive liquid crystal light valves, and the power supply unit that supplies a power to the respective units of the projector. Further, a projector has been suggested in which a plurality of fans functioning as cooling units are provided such that temperatures of the heat emission portions do not exceed respective rated temperature values.
For example, a three-plate-type projector that has been disclosed in JP-A-2000-221599 has a structure in which exclusive cooling fans are respectively provided in a light source, light modulating elements, a lamp driving unit, and a power supply unit. In particular, in regards to the light modulating elements, an exclusive fan is provided for each of liquid crystal light valves for red, green, and blue. That is, three fans are provided therein. Further, if the plurality of fans includes a large-scaled fan that exhausts air heated by each heat emission portion when the plurality of fans blow the air to the outside of the projector, total seven cooling fans are provided in the projector.
FIG. 8 is a schematic plan view mainly illustrating a cooling structure in a projector according to the related art.
However, if seven fans are provided in one projector, the number of components is increased, the manufacturing cost is increased, and noises and power consumption may be increased. A projector 200 shown in FIG. 8 has been suggested in order to solve the above-described problems.
The projector 200 includes a fan F1 that cools down a light source unit 5, two fans F2 and F3 that cool down a light modulating unit 30 including three liquid crystal light valves 23R, 23G, and 23B, a fan F4 that simultaneously cools down a cower supply unit 40 and a lamp driving unit 45 as one set, and a fan F5 that exhausts air heated by each heat emission portion when the plurality of fans blow the air to the outside of the projector. That is, the projector 200 includes the five fans. In particular, in the projector, the power supply unit 40 and the lamp driving unit 45 are provided to be adjacent to each other as one set, and are simultaneously cooled down by one fan F4. Specifically, a cooling air Wa that is blown by the fan F4 is substantially equally distributed to a cooling air W1 toward the power supply unit 40 and a cooling air W2 toward the lamp driving unit 45.
According to this structure, the projector 200 can perform a necessary cooling process while reducing the number of fans, which reduces the noises and the power consumption.
Further, the projector 200 is provided such that a plurality of color modes can be set according to projection environments. The projector 200 adjusts luminance of the light source unit 5 according to a selected color mode. Examples of the color modes include a dynamic mode which is suitable for viewing images in bright rooms, or a theater mode which is suitable for enjoying images of great depth in dark illumination environments. When the dynamic mode is selected, a driving power of the discharge lamp 1 from the light source unit 5 is increased to increase luminance. In contrast, when the theater mode is set, the driving power of the discharge lamp 1 is decreased to decrease the luminance.
As such, since an amount of power supplied to the discharge lamp 1 is changed according to the selected color mode, amounts of heat emitted from the power supply unit 40 and the lamp driving unit 45 are also changed. For this reason, the revolution number of the fan F4 is also changed according to the selected color mode, such that the power supply unit 40 and the lamp driving unit 45 are appropriately cooled down.
However, in the projector 200 according to the related art, the power supply unit 40 and the lamp driving unit 45 are cooled down in a state where the air volumes of the blowing winds by the one fan F4 are substantially equally distributed to the power supply unit 40 and the lamp driving unit 45. For this reason, if the temperature difference between the power supply unit 40 and the lamp driving unit 45 is generated, it is necessary to drive the fan F4 according to the temperature of the side having the high temperature between the power supply unit 40 and the lamp driving unit 45. As a result, the revolution number of the fan F4 is increased, which increases the noises and the driving power.
FIG. 9 is a graph illustrating temperature states of a power supply unit and a lamp driving unit according to a driving power (luminance) of a light source unit in a projector according to the related art.
In a graph g, a horizontal axis indicates a driving power (luminance) of the discharge lamp 1, a longitudinal axis (left side) indicates temperatures of the power supply unit 40 and the lamp driving unit 45, and a longitudinal axis (right side) indicates a driving voltage of the fan F4. The graphs shown by a solid line and a broken line indicate the temperature variations in the power supply unit 40 and the lamp driving unit 45, respectively. A bar graph indicates a driving voltage of the fan F4. Further, since the driving power of the discharge lamp 1 is in proportional to the luminance and the driving voltage of the fan F4 is in proportional to the air volume, it is possible to obtain and use the driving power of the discharge lamp 1 as the luminance and the driving voltage of the fan F4 as the air volume.
When the theater mode is selected and the luminance is decreased, since the temperature at the lamp driving unit 45 becomes higher than the temperature at the power supply unit 40, the fan F4 rotates with a driving voltage (7.5 V) that is determined on the basis of an air volume necessary for the cooling air W2 of the lamp driving unit 45 having the high temperature. Meanwhile, when the dynamic mode is selected and the luminance is increased, since the temperature at the power supply unit 40 becomes higher than the temperature at the lamp driving unit 45, the fan F4 rotates with a driving voltage (9 V) that is determined on the basis of an air volume necessary for the cooling air W1 of the power supply unit 40 having the high temperature.
Further, since the fan F4 is provided near the outer mounting surface of the projector 200 to efficiently intake the air from the outside, the fan is disposed with a dust-proof filter (not shown) therebetween, as compared with the fans F2 and F3 disposed in the projector, but operation sounds may easily leak to the outside.
Further, the temperature characteristics of the lamp driving unit 45 are in inverse proportion to the driving power of the discharge lamp 1. The reason results from the characteristics of the discharge lamp 1. Specifically, according to the characteristics of the discharge lamp 1, even if the driving voltage is decreased to suppress a light amount of the discharge lamp 1, a predetermined amount of power including a loss power is necessary for maintaining a turned-on state of the discharge lamp 1, that is, a discharge state of the discharge lamp 1. For this reason, even when the driving voltage is decreased, a load of the lamp driving unit 45 is rarely decreased. Further, the fact that the luminance is decreased while the air volume necessary for cooling is ensured, and thus the driving voltage of the fan F4 is decreased and the air volume of the cooling air W2 is decreased also becomes one factor of the reason.
As such, in the projector 200 according to the related art, the power supply unit 40 and the lamp driving unit 45 each having a different temperature characteristic are cooled down with the driving voltage based on the temperature of the side having the high temperature between the power supply unit 40 and the lamp driving unit 45, which increases noises and deteriorates energy utilization efficiency.